BIO 313: Cell and Molecular Biology (Prof. Jea Farida R. Guroalim) Laboratory Exercise No. 1 Visualizing Cells Name: ________________________________ Date & Time: ____________ Lab Objectives: review the major organelles of eukaryotes investigate plant cell structures discover how chloroplasts while undergoing photosynthesis identify easily identifiable organelles within human cells conduct a gram stain to visualize bacteria Materials: Microscope Extension wire Forceps Syringe Glass slides Cover slips Petri dish Agar Paper towel Iodine solution Safranin Dropper Specimens Gloves Googles Methylene blue Procedure: Exercise A: Eukaryotic Organelles Experiment 1: Investigating Plant Cells Part 1: The Onion Cell Biologists frequently study the onion cell because onions are readily available and their cells provide a clear view of all the basic characteristics of plant cell structure. The onion's large cells can be seen easily under a microscope and also used to teach the fundamentals of cell biology. The skin (or epidermis) between the dormant leaves of an onion are a single cell thick, and serve as a classic representation of the internal structure of plant cells. In fact, the term "cell" came from a pioneer of microscopic biology, Robert Hooke, while looking at epidermal onion cells under a microscope. He thought these structures resembled the cells that monks would sleep in. Instructions: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. Prepare onion wet mount. Quarter an onion. Isolate a single onion leaf. Break leaf in half and pull thin layer of epidermis, being careful to not let it fold on itself. If it does fold, attempt to unfold it. You may want to use forceps. Place the flattened onion epidermis on a microscope slide. Place a small drop of iodine on the epidermis. Iodine will stain the nucleus of the cell so it is visible. Place cover slip on top of the specimen. With a paper towel, remove any excess iodine. Place wet mount on microscope. With the scanning objective (4x), focus the specimen and locate a section where the epidermis is a single cell thick. This is usually found on the edges of the specimen. Switch to low power objective (10x). Focus in on a section of the epidermis where it is a single cell thick. Switch to high power objective (40x) and focus, only with the fine focus knob. Questions/Activity: 1. 2. 3. 4. Draw the onion cell as viewed in the microscope and label the parts. List down the parts and enumerate its functions. Identify whether your onion cells have chloroplasts or not, and discuss why? What have you learned from this exercise? Part 2: Cytoplasmic Streaming in Elodea Elodea is an freshwater, aquatic plant native to the Americas commonly used in aquariums. With leaves only two cells thick. Elodea is a good model to study living plant cells in action. In this experiment, you will see chloroplasts moving in the Elodea cells as they begin to photosynthesize. This movement is known as cytoplasmic streaming, which distributes nutrients more evenly throughout the cell. Imagine if most of the chloroplasts within a plant cell were concentrated within a part of the cell. Molecules essential for photosynthesis (i.e. carbon dioxide) would quickly be metabolized. This would leave an unequal distribution of carbon dioxide in the cell. Movement of the organelles around the vacuole allows for a more even distribution of molecules necessary for the cell's essential biochemical pathways. It has also been suggested cytoplasmic streaming, allows greater efficiency of photosynthesis, by increasing overall light absorption. Instructions: 1. 2. 3. 4. 5. Store Elodea in a dark place for at least one hour. Prepare a wet mount of Elodea. Select a leaf from an Elodea plant. Place the leaf on a microscope slide. Place a drop of water on the leaf and place a cover slip over the specimen. Push the cover slip down and use a paper towel to remove excess water. 6. Focus the Elodea under scanning objective. Switch objectives to low section near the edge attempting to find a section where the cells are a single layer thick. Switch to high objective and refocus with the fine adjustment knob. 7. Turn on the light source of the compound microscope to full intensity. This will allow the chloroplast to begin to undergo photosynthesis. Leave the wet mount of Elodea under the light for 15-20 minutes. 8. After 15-20 minutes, reduce the light so that you may visualize the Elodea cells. You should see the chloroplasts moving in a circular pattern around the cell. This process is known as cytoplasmic streaming. Questions/Activity: 1. Draw the plant cell as viewed in the microscope and label the parts. 2. List down the parts and enumerate its functions. 3. Analyze how cytoplasmic streaming occurred in your cells (or from the video for online classes). Did it happen? Why is it happening? How are the chloroplasts moving through the cell? 4. What have you learned from this exercise? Experiment 2: Investigating Animal Cells Part 1: Cheek Cell Cheek cells are epithelial cells that line the interior surface of our mouths. The base layer of cells in an epithelial structure are not actually cells, but a sticky layer on which the cells anchor. The other surface of the epithelial cell touches the outside world (like skin) or an open space (like the mouth). Because of their high rate of division, epithelial cells are found tightly packed together. When you stain your cheek cells, you should be able to distinguish between the nucleus, cytoplasm, cell membrane. If you are very observant (and lucky) you may visualize the nucleolus and other organelles with in the cell. Instructions: 1. Using a flat toothpick, very gently scrape the inside of your cheek to obtain cheek cells. 2. Spread the cells on the end of the toothpick onto the microscope slide. 3. Add 1 small drop of methylene blue to the sample. Methylene blue will stain the sample, allowing visualization of the nucleus, cytoplasm, and even some organelles. Note: methylene blue will stain your hands and clothing. Wear goggles, gloves and an apron. 4. Place a cover slip on the sample. Press down on the coverslip and remove excess methylene blue with a paper towel. 5. Using the scanning objective (4x), focus the specimen and locate cheek cells. Change the objective to low power, refocus on a few cheek cells. 6. Finally, visualize your cheek cells at high power. At this point you may need to reduce your light intensity and adjust the condenser aperture. Questions/Activity: 1. 2. 3. 4. Draw the human cheek cell as viewed in the microscope and label the parts. List down the parts and enumerate its functions. How do you describe cheek cell? What have you learned from this exercise? Part 2: Blood Cell Human blood appears to be a red liquid to the naked eye, but under a microscope we can see that it contains four distinct elements. Instructions: Caution! Blood can carry diseases that can be transferred from person to person. One should always avoid coming into contact with another person's blood. If it is unavoidable, one should wear rubber gloves. 1. Massage your finger and dab some alcohol. Next, using a syringe, poke your little finger quickly and lightly. Squeeze your finger and place a drop of blood on a slide and cover with the coverslip. (Use a band-aid to prevent infection.) 2. Place the slide on the microscope stage, and bring into focus on low power (100X). Adjust lighting and then switch into high power (400X). 3. You should see hundreds of tiny red blood cells; there are billions circulating throughout our blood stream. Red blood cells contain no nucleus, which means they can't divide. Red blood cells are constantly produced by the bone marrow and the spleen. You should also be to find a few white blood cells. They are slightly larger than red blood cells, and have a nucleus. They resemble an amoeba and can contort their body in any way they like. White blood cells fight infection by consuming foreign bodies. The platelets are fragments of red blood cells and are very small. 4. The person whose blood was examined should then clean the slide. Avoid coming into contact with another person's blood. Questions/Activity: 1. 2. 3. 4. Draw the blood cell as viewed in the microscope and label. List down the parts and enumerate its functions. How do you describe blood cells? What have you learned from this exercise? General Questions: 1. 2. 3. 4. What are the main structural features of eukaryotic cells? What distinguishes animal cells from plant cells? What are mitochondria? What are chloroplasts?
